Preparation of aminotriazine-aldehyde condensation products



Patented Feb. 29, 1944 PREPARATION OF AMINOTRIAZINE-ALDE- HYDECONDENSATION PRODUCTS Robert C. Swain, Riverside, and Pierrepont Adams,Stamford, Conn., assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine No Drawing. Application February 27, 1941,Serial No. 380,894

3 Claims.

of water by azeotropic distillation. The dehydration is a time-consumingstep which adds considerably to the cost of the process. Althoughparaformaldehyde may be used in the process in place of aqueousformaldehyde to avoid the necessity of removing water added through theformaldehyde solution, its high cost limits its use to special cases.Until recently, aqueous formaldehyde solutions containing more thanabout .37% formaldehyde by weight were not commercially obtainable, andeven those containing this concentration of formaldehyde required thepresence of a stabilizer to prevent formation of paraformaldehyde.Methanol in amounts of 8 to 12% is commercially used as a stabilizer.The addition of methanol to aqueous formaldehyde solutions adds tothecost of the formaldehyde and its presence in the melamine-formaldehydereaction mixture is objectionable for several reasons. Melamine appearsto dissolve more slowly in formaldehyde solutions in the presence ofmethanol. Another of the disadvantages occasioned by the use ofmethanol-stabilized formaldehyde in the process of preparing alkylatedaminotriazlne-aldehyde condensation products is the formation of aternary distillate in the dehydration step of the process. Water isremoved from the condensation product by azeotropicaily distilling offfrom the reaction mixture water and a solvent, which may also be thealkylating agent, such as butanol. When methanol is present, however,the distillate is a ternary mixture of methanol, water and solvent fromwhich it is dimcult to recover the solvent for reuse in the process.

Aqueous formaldehyde of 30% strength may be obtained in which nostabilizer is required, but the use of solutions of this strengthrequires the removal of large quantities of water in the azeotropicdistillation, and? prolonged heating period is necessitated which tendsto increase the viscosity of the resin solution to an undesirabledegree. The speed of reaction is also lowered due to the lowconcentration of formaldehyde, and the capacity of the plant is reducedon acstep.

count of the increased time of reaction and increased volumes of waterto be accommodated in the reaction vessels.

In our copending application, Serial No. 306,- 516, filed November 28,1939, now Patent No. 2,237,092, we described a method of stabilizingstrong aqueous formaldehyde solutions by the addition thereto ofmelamine or methylol melamines in amounts of about 1 to 10%. As pointedout in that application, it is possible to obtain stable solutions ofhigh formaldehyde content by the simple expedient of dissolving thereinmelamine or methylol melamines. The melamine may be dissolved in theaqueous formaldehyde solutions, preferably by adding themelamine andheating to Gil- C. for a short time. One percent of melamine dissolvedin a formaldehyde solution will have a definite stabilizing effect,while 6% of melamine can stabilize a 50% solution of formaldehyde for aperiod of many months, even when stored at low temperatures. Although itis possible to dissolve more than 10% of melamine in aqueousformaldehyde, it is, in general, not desirable to do so because of thepossible formation of a gel, as described in our copendlng application.

We have now discovered that many of the disadvantages of previouslyknown methods of preparing alkylated aminotriazine-formaldehydecondensation products may be overcome and a superior product obtained ina cheaper and better way when formaldehyde solutions stabilized withmelamine or methylol melamines are employed. This is particularly trueof the strong aqueous solutions of 40-50% formaldehyde content by weightthat are described in our above mentioned application.

For some reason not clearly understood at present, the clear alkylatedmelamine-formaldehyde lacquers prepared according to our process aremore stable upon storage than similar lacquers prepared in the same waybut with formaldehyde solutions containing methanol. We

also find that melamine-stabilized formaldehyde will dissolve themelamine or other aminotriazine more rapidly than willmethanol-stabilized formaldehyde, due, perhaps, to an interfering actionof the methanol. 0! great practical importance is the improvement in thecharacter of the azeotropic distillate obtained in the dehydration stepwhen using our melamine-stabilized formaldehyde in place ofmethanol-containihg formaldehyde.- We find that when alcohols partiallyimmiscible with water are used in the alkylating such as butanol. theazeotropic distillate separates sharply which greatly simplifies therecovery of the organic solvent fraction. When using butanol as theorganic solvent inthe azeotropic distillation we find that thedistillate immediately separates into two layers; one composed of watercontaining approximately 8% butanol, and the other containingapproximately 80% butanol and 20% water. We are thus enabled, during thefirst stages of the dehydration, to return the butanol fraction directlyto the reaction vessel without an intermediate fractionation step. Whenmethanol is present, as from methanol-stabilized formaldehyde, it actsas a mutual solvent for the water and butanol and the azeotropicdistillate is more complex which makes it dimcult to reuse the butanolin the dehydration step without first removing the water and methanol.Processing the butanol to recover it is greatly simplifled by the use ofour methanol-free melaminestabilized formaldehyde.

When using methanol-free melamine-stabilized formaldehyde solutions of35 to 4.0% strength, we find the principal advantage to lie in thesimplification of the azeotropic distillate, which, as pointed outabove, consists simply of two phases which separate easily, thus greatlysimplifying the recovery of the solvent. Also, the melamine employed inthe reaction dissolves more readily and the resin solution produced isof materially greater stability.

We prefer to use formaldehyde solutions of fairly high strength, such as40 to 50% formaldehyde, as we find that the use of concentratedmethanol-free formaldehyde reduces considerably the time required forthe melamine-formaldehyde reaction to take place. We also find that weare enabled to obtain a larger production capacity from our reactionvessels due to the shortened time period and greater concentration ofactive materials which they are able to contain. Further, sinceconsiderably less water is present, as compared to the use offormaldehyde hitherto available, the dehydration step is materiallyshortened as to time and simplified in procedure.

It is evident from the foregoing that melaminestabilized formaldehydesolutions, particularly those of 40 to 50% formaldehyde content, may beemployed to great advantage in the manufacture of alkylatedmelamine-formaldehyde condensation products. In the condensationreaction we may use any aminotriazine such as melamine, formoguanamine,ammeline, monoamino- 1,3,5-triazine, monomethyl diamino-1,3,5-triazine,phenyl diamino-1,3,5-triazine, and the like, either singly or inadmixture. Ordinarily, we use about 5 moles of formaldehyde for eachmole of triazine, but the formaldehyde may be used in amounts rangingfrom about 2 /2 moles to 6 or more moles for each mole of aminotriazine.The alkylating agent may be any primary alcohol such as amyl, butyl,octyl, etc.

The following specific examples illustrate in greater detail some of themany modifications to which our invention is susceptible, and it is tobe understood that they are given merely to aid in more fullyunderstanding the manner of carrying out our present invention and notin limitation thereof. Parts given are by weight Example 1 and at onceinto two layers,v

NaOH. 111.5 parts by weight of melamine was then added with agitation tothe formaldehyde and the mixture heated in 35 minutes to 76 C. To theresulting clear solution was added slowly 440 parts by weight of normalbutyl alcohol containing 0.30 part by weight of 87% formic acid. Duringthe .addition of the acidified alcohol, which required 30 minutes, thetemperature of the contents of the reaction vessel ,was' maintainedbetween '20 and 80" c. The water in the mixture was then removed byazeotropic distillation of water-butyl alcohol with frequent additionsof dry butyl alcohol to replace the alcohol distilled off. When thevapor temperature reached 100 C., 275 parts of dry butyl alcohol hadbeen added and 317.5 parts by weight of distillate removed. A vacuum of29 inches of Hg was then applied to the system and the distillationcontinued at a lower temperature until 380 parts by weight of distillatewere removed under vacu To the resin remaining in the reaction vesselwas added 16.4 parts by weight of anhydrous butyl alcohol and 158.1parts by weight of xylene. The resin solution was then filtered to yielda product containing 50% solid resin, 25% butyl alcohol and 25% xylene,with a viscosity at 25 C. on the Gardner-Holdt scale of V-W anda mineralspirit tolerance of 2.1-1.

Example 2 405 parts by weight of a 37% methanol-free aqueous solution offormaldehyde stabilized with 2% by weight of melamine, 375 parts byweight of butanol, 118 parts by weight of melamine and 1 part oftributylamine were added to a vessel fitted with an agitator,thermometer, and reflux condenser. The contents of the vessel wereheated, and in 18 minutes at a temperature of C. the melamine wascompletely dissolved. The reaction mixture was heated to C. underrefluxing conditions, for 15 minutes, whereupon 0.9 part by weight of85% HaPO4 dissolved in parts by weight of butanol was added. The mixturewas then allowed to distill. The distillate consisting of an azeotropicmixture of butanol and water separated cleanly into two layers. As thedistillation continued a total of 500 parts of butanol were added fromtime to time in small portions. After one hour and 51 minutes ofdistillation the temperature of the vapor was 96 C. and 551 parts byweight of the azeotropic mixture had been collected. A vacuum was thenapplied to the system and the distillation continued for 22 minutes at87 0. Heating was discontinued and the resin poured from the reactionvessel and filtered.

The same procedure as described above was employed in another run,except that 405 parts of a 37% aqueous solution of formaldehydestabilized with 10% methanol was used instead of 405 parts of melaminestabilized formaldehyde. It was observed that the melamine dissolvedmuch more slowly in the presence of methanol, less butanol was distilledoff in an equivalent period of distillation, and the distillate did notseparate as readily into butanol and aqueous layers.

Example 3 152 parts by weight of an aqueous solution of formaldehydecontaining 50% formaldehyde and 7% melamine and'having a pH of 3.7 washeated to 85 C. with 53 parts of melamine until the melamine wasdissolved. 300 parts by weight of butanol was then added slowly over aperiod of 70 minutes, while heating at 95 C. Water and butyl alcoholwere then distilled off and dry butanol was added from time to time toreplace the distillate removed. Distillation was completed under avacuum of 25 inches of mercury. 75 parts by weight of xylene was thenadded and the resin solution filtered. The finished lacquer contained50% solids, had a viscosity of Y on the Gardner-Holdt scale, and amineral spirits toler ance of 2.8-1.

Example 4 300 parts by weight of an aqueous solution of formaldehydecontaining 47.7% formaldehyde and stabilized with 6.3% melamine washeated with 106 parts by Weight of melamine until the melamine wasdissolved and the pH of the solution then adjusted to 7.1 with diluteNaOH. 400 parts byweight of dry butanol containing 0.25 part by weightof methyl acid phosphate, as catalyst, was then slowly added withagitation and heating at about 65 C. After addition of the butanol andcatalyst and upon heating for 20 minutes the reaction mixture wasdistilled to remove water. During distillation, 400 parts by weight ofanhydrous butanol was added. During the last stages of distillation a,vacuum was applied to reduce the distillation temperature and preventundue polymerization of the resin. Distillation was continued until 475parts by weight of fluid resin remained in the reaction vessel. 100parts by weight of xylene was then added to reduce the solids content to50.5%. The filtered lacquer had a viscosity at 25 C. of U-V and amineral spirits tolerance of 2.0-1.

The clear resin solutions obtained as described in the foregoingexamples may be used as clear lacquers or adhesives or may be blendedwith other resinous compositions, drying oils, cellulosic derivatives,plasticizers, solvents, pigments, driers, fillers, etc., in the mannerdescribed in the U. S. Patent to L. P. Moore No. 2,218,474, of October15, 1940. Obviously, many modifications and variations may be made inthe process described above without departing from the spirit and scopeof the invention as defined in the appended claims.

What we claim is:

1. A method of preparing alkylated melamineformaldehyde condensationproducts which comprises heating together in a reaction vessel amethanol-free aqueous solution of formaldehyde containing -50% by weightof formaldehyde and 1-10% by weight of melamine dissolved therein,melamine in molecular ratio of 2.5-6 moles of formaldehyde foreach moleof melamine, and a water-immiscible primary alcohol, thereafter removingthe water from the reaction mixture by azeotropic distillation,separating the water immiscible alcohol from the aqueous portion of thedistillate and returning the alcohol to the reaction vessel.

2. A method of preparing butylated melamineformaldehyde condensationproducts which comprises heating together in a reaction vessel 8.methanol-free aqueous solution of formaldehyde containing 35-50% byweight of formaldehyde and 1-10% by weight of melamine dissolvedtherein, melamine in the molecular ratio of 2.5-6 moles of formaldehydefor each mole of melamine, and n-butyl alcohol, thereafter dehydratingthe resin solution by azeotropic distillation, separating the n-butylalcohol from the aqueous portion of the distillate and returning then-butyl alcohol to the reaction vessel.

3. A method of preparing alkyiated melamineformaldehyde condensationproducts which comprises heating together in a reaction vessel amethanol-free aqueous solution containing to by weight of formaldehydeand 1 to 10% by weight of melamine, melamine in the molecular ratio ofabout 5 moles of formaldehyde to each mole of melamine, and awater-immiscible primary alkyl alcohol, thereafter dehydrating theresulting resin solution by azeotropic distillation, separating thewater immiscible alcohol from the aqueous portion of the distillate andreturning the alcohol to the reaction vessel.

ROBERT C. SWAIN. PIERREPONT ADAMS.

